1. Technical Field
The present invention relates to a ballpoint pen ink containing a lubricating component. The present invention also relates to a ballpoint pen using the ink and having a ballpoint pen tip comprising at least a ball as a writing member and a ball holder holding the ball in the state of the ball being partially projected from the front-end opening.
2. Background Art
In order to obtain a ballpoint pen ink ensuring a soft and smooth writing feel, attempts to adjust the viscosity of the ink or add a material imparting lubricity to the ink have been made.
When the viscosity of the ink is reduced by adjusting the amount of the thickener added, since the resistance to rotation of the ball decreases in writing, there is an advantage which allows for writing with a soft writing feel. However, since the ink has a low viscosity, the ink film formed between the ball and the ball receiving seat to easily moves by writing pressure, and an uneven feel due to direct hitting of the ball on the ball receiving seat during writing is transmitted to the hand, as a result, the writing lacks a smooth feel.
On the other hand, when the viscosity of the ink is raised by adding a resin or the like and the thickness of the ink film formed between the ball and the ball receiving seat is increased, although a smooth writing feel may be obtained, rotation of the ball is subject to large resistance due to low fluidity of the ink to give a heavy writing feel.
Also, for satisfying both a soft feel and a smooth feel in writing, an attempt to impart pseudo-plastic viscosity characteristics to the ink by using a shear-thinning agent which imparts viscosity has been made so as to lower the viscosity by a high shear force applied to the ink due to rotation of the ball during writing and to reduce the rotation resistance of the ball (Patent Document 1, from page 2, right column, line 36 to page 3, right column, line 23).
Furthermore, when a material for imparting lubricity to the ink, such as phosphoric acid ester (Patent Document 2, from page 2, right column, line 32 to page 3, right column, line 30), dipolyoxyethylene alkyl ether phosphoric acid and tripolyoxyethylene alkyl ether phosphoric acid (Patent Document 3, from page 2, right column, line 23 to page 3, right column, line 15), is added to the ink, the frictional resistance between the ball and the ball receiving seat during writing is reduced and a smooth writing feel is obtained. An attempt to obtain softer and smoother writing by combining such a material for imparting lubricity to the ink and a thickener for adjusting the viscosity has been also made (Patent Document 4, from page 2, left column, line 28 to page 3, left column, line 26). Additionally, an attempt to add polyoxyethylene hardened castor oil that is a new pen starvation inhibitor but has a lubricating effect (Patent Document 5, from page 1, column 2, line 15 to page 2, column 3, line 2) or an attempt to add polyoxyalkylene hardened castor oil and an unsaturated fatty acid in which the carbon number of a hydrocarbon group bound to a carboxyl group is 17 or more (Patent document 6, from page 3, line 3 to page 3, line 5), has been also made.
In order to obtain a ballpoint pen with a good writing feel, a ballpoint pen wherein the diameter of the ball receiving seat part and the diameter of the center hole are specified has been disclosed in the invention of JP-U1-2-022883 (Patent Document 7, claims).
Furthermore, a ballpoint pen wherein the projected area of the ball seat is specified so as to obtain a smooth and soft writing feel is disclosed in the invention of JP-A-8-252998 (Patent Document 8, claims).